With development of the science and technologies, computers have become indispensible to people's daily life. As has been known, there are mainly two kinds of structures for power supplies disposed in the computers. As shown in FIG. 1, a power supply 10 comprises a housing 11, a circuit board 12 and a fan assembly 13. The circuit board 12 is disposed inside the housing 11, and is adapted to bear an electronic component 121 necessary for operation of the power supply 10. The housing 11 has an air outlet 14 disposed at a side thereof. The fan assembly 13 is disposed perpendicular to a surface of the circuit board 12, and the air produced by the fan assembly 13 acts on the circuit board 12 in parallel in a direction D1. After absorbing heat from the electronic component 121 on the circuit board 12, the air produced by a fan body 131 becomes hot air, which then flows out in a direction D4 via the air outlet 14. China Patent No. ZL200420082974.0 discloses a similar embodiment. However, because the air produced by the fan assembly 13 flows from one side to the other side of the circuit board 12, the air will have a poor effect of dissipating heat from the electronic component 121 when flowing to the side away from the fan assembly 13.
As shown in FIG. 2, a power supply 20 comprises a housing 21, a circuit board 22 and a fan assembly 23. The circuit board 22 is disposed inside the housing 21, and is adapted to bear an electronic component 221 necessary for operation of the power supply 20. The housing 21 has an air outlet 24 disposed at a side thereof. The fan assembly 23 and the circuit board 22 are disposed opposite to each other inside the housing 21. The air produced by the fan assembly 23 acts on the circuit board 22 perpendicularly in a direction D2. However, after having cooled the electronic component 221 on the circuit board 22, the air produced by the fan assembly 23 cannot completely flow out in the direction D4 via the air outlet 24; and instead, a part of the air is bounced back intensively, which has a great influence on the heat dissipation effect.